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SubjectRe: Linux for JavaVM
It was design to run several MVS os. For example on a single CPU one
could have a production system as well as a test environment. This allow
a company from purchase a second CPU.

On Wed, 8 Jan 1997, John G. Alvord wrote:

> On Tue, 07 Jan 97 22:00:17 +1000, wrote:
> > Running Linux in Linux in Linux would be a great thing! I've been reading
> >reports about how IBM's older mainframes worked and specifically about the
> >architecture of VM/DOS. Apparently they had a virtual machine which the OS ran
> >in, the VM provided file access and linear memory to the OS.
> I did a lot of work on that system, called VM. There was a control
> program (CP) which ran virtual machines. It was all written in S/370
> assembler and was about 300K lines of code (VM and the user interface
> called CMS which had a file system, an exec language, and little else).
> Of course that excludes compilers, etc.
> Most of the work was a detailed simulation of memory and I/O. S/370 I/O
> is complex, involving channel programs (you don't want to know). It also
> simulated privileged instructions. The result was sufficient to run VM
> under VM, which was a marvelous development environment. Imagine single
> stepping, breakpointing, etc at the kernel level.
> A big project to duplicate. Incidently, VM still exists and is being
> enhanced even today.
> john alvord

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